This invention relates to novel chlorosulfonated polyethylene materials and methods of preparation thereof. More particularly, the present invention relates to a finely-divided, particulate chlorosulfonated material having a weight average molecular weight of from about 40,000 to about 300,000 and a 100 percent modulus, measured in accordance with American Society for Testing and Materials (ASTM) Test D-412 of from about 0.6 to about 4.8 megapascals (MPa).
Chlorosulfonated polyethylene materials in general and various processes for preparing such materials are known. Chlorosulfonated polymers are manufactured commercially in an inert volatile solvent by simultaneously (a) chlorinating polyethylene to replace hydrogen by chlorine and (b) reacting the chlorinated polyethylene with a mixture of chlorine and sulfur dioxide to introduce chlorosulfonic groups into the chlorinated polymer. This procedure is described in detail in U.S. Pat. No. 3,296,222 issued to Dixon et al.
Chlorosulfonation of a polyethylene starting material with sulfuryl chloride in a single phase in solution is described in U.S. Pat. No. 3,299,014.
Chlorosulfonation in solution is not, however, a problem-free process. Solvents used in commercial processes to dissolve both polyethylene and the chlorosulfonated product are generally not volatile enough to be vaporized by the heat of reaction. Accordingly, it is necessary to heat the mixture of solvent and chlorinated product to remove the solvent. This is a slow and expensive procedure.
Noeske et al., in U.S. Pat. No. 2,889,259, disclose a process for the chlorosulfonation of a polyethylene starting material having a molecular weight of 80,000 to 1,400,000. The process involves fluidization of the starting material with a gaseous mixture of sulfur dioxide and chlorine at a temperature not substantially in excess of 100.degree. Centigrade. Introduction of the gaseous mixture with ultraviolet light may enhance the chloro-sulfonation reaction. The temperature is generally within the range of 40.degree. to 80.degree. Centlgrade. The gaseous mixture typically has a ratio of sulfur dioxide to chlorine of 1:1 to 2:1. The process provides reaction products having a sulfur content as high as about 10 percent by weight and a chlorine content as high as about 20 percent by weight. Noeske et al. state that treatment with gaseous chlorine before and/or after chloro-sulfonation raises the chlorine content to as high as 50 percent by weight.
Chlorosulfonated materials prepared in accordance with the teachings of Noeske et al. are generally not amorphous materials. That is, the materials have sufficient residual crystallinity to render them relatively inflexible and non-elastomeric.
Eckardt et al., in U.S. Pat. No. 3,542,746, disclose a two-stage process for preparing high molecular weight chlorosulfonated polyethylene. In a first stage, high density, high molecular weight polyethylene is chlorinated to a chlorine content of about 20-50 percent by weight using a procedure which reduces crystallinity of the polymer to less that one percent as determined by differential thermal analysis. In a second stage, the chlorinated polymer is treated with a mixture of sulfur dioxide and chlorine to substitute sulfonyl chloride groups on the polymer. This treatment is carried out at a temperature of 0.degree.-100.degree. Centigrade, either in the dark or catalyzed with actinic light, with a ratio of sulfur dioxide to chlorine in the range of 20:1 to 1:10. The two-stage process produces polymers which are substantially amorphous and which contain 25-50 percent by weight of chlorine and 0.6 to 1.5 percent by weight of sulfur. By "high molecular weight" Eckardt et al. refer to weight average molecular weights in the range of about 500,000 to 5,000,000, preferably 700,000 to 3,500,000.
Chlorosulfonated materials prepared in accordance with the teachings of Eckardt et al. have been found to be difficult, if not impossible, to process on equipment generally used in the rubber industry such as two-roll compounding mills, high intensity mixers and the like.